Control system



Dec. 18, 1928.

C. LE G. FORTESCUE CONTROL SYSTEM Original Filed Feb. 5. 1921 2Sheets-Sheet 1 WITNESSES:

fi/m. x /6M INVENTOR Char/es LcG. l orlescue.

w BY AfTORNEY Dec. 18, 1928. 1,695,891

c. LE G. 'FORTESCUE CONTROL SYSTEM Origiqal Filed Feb. 5, 1921 2 s ..s g

Wli'NESSES: INVENTOR I 7/ Char/eslafibrtasczzet BY 1 v w 'vide aplurality of-conductor Patented Dec. 18, 1928.

UNITED STATES. PATENT OFFICE.

CHARLES LE G. FORTESCUE, OI PITTSBURGH, PENNSYLVANIA, ASSIGNOR TO WEST-INGHOUSE 'ELECTRZIC &*MANUFACTUBING COMPANY, A CORPORATION OF PENN-SYLVANIA.

CONTROL SYSTEM.

Original application filed February 5, 1321, Serial-No. 442,764. Dividedand this application filed August 28, 1925.

My invention relates to polyphase motors and it has special relation toa system of acceleration therefor. 1

One object of my invention is to provide a system whereby a smoother andmore gradual acceleration of the motor or motors shall be,

accomplished than has heretofore been'possible.

Another object of my invention is to propaths for the current from eachphase winding, utilizing, however, various combinations of the samepaths for the different currents.

A further object of my invention isto provide a method of accelerationfor a plurality of motors which will not affect the balanced pullingtorque of the motors.

A still further object of my invention is to provide a method oztconnectingthe secondary windings of a plurality of motors toa singleresistor or to a plurality of resistors so that there will be nointerchange of currents between the motors,

It is a further object ofmy inventionto enable a plurality ofmotorsof-difl'erent phase relation to be properly controlled fromaasingle rheostat.

Other and more specific objects of my in vention will be apparent fromthefollowing description and claims.

The present invention will hereinafter be described as applied to thesecondary windings of polyphase inductionmotorsbut it will be understoodto be equally applicable to other alternatingrurrent motors and toprimary, as well as to secondary, windings.

In the control of induction motors, theeffective speed of a motor beyonda predetermined point depends uponthe total resistance in circuit withthe secondary windings thereof.

As is well known, the efiect of resistance in circuit with the secondarwinding is to increase the slip between t eprimary and sec ondarywindings to delay the full-speed .operation of the motor. However, whenstarting, it isdesirable to increase the rotor-circuit resistance toproducethe maximum torque. At the same time, it is also desirable toeconomize, as far as possible, in the amount of resistance that isinserted, without impairing the efliciency of the motors. Accordingly,

Serial No. 53,061.

windings, any change in its value, which may be effected byshort-circuiting a section of it, will affect the current flowing inboth of the phase windings. Therefore, by varying the ohmic value of asingle resistor connected in circuit with the t-wo'secondary phasewindings of a motor, the same results may be obtained as is effected byvarying simultaneously the ohmic value of two separate resistors eachconnected in circuit with a different secondary phase winding.

By the application of this principle to. the acceleration of polyphaseinduction ,motors, it is ossible to obtain, with a relativelysmallnumlier of switches, the results heretofore obtained with a. relativelylarge number of switches.

The desired result for one or more motors is secured by using a type ofresistor wherein the resistor sections haveno common terminal but areall connected to form a continuous resistance path to which .each of thesecondary phase windings is connected.

The acceleration is shown as accomplished by the use of electromagneticswitches but any of the wellknown methodsof short-cin cuiting resistorsmay be used without afiecting the result obtained by the principles ofthe present invention. A

The present invention will best be under stood byreferenceto theaccompanying drawings, wherein Figure 1 is a diagrammatic view of oneform of circuits and apparatus embodying myinve ntion Fig.2 is adiagrammatic view of a modified form of circuits and apparatus embodiedin my invention, as applied to two motors and utilizing two resistors;and

Referring to Fig. 1, a two-phase induction motor 10, having primary orstator windings 11 and secondary or rotor windings 12, is shown. Theprimary windings are energized connect ing? 21 In order to hold 1 O O OO t S V. r e 7 1A D U other ways for connecting these switches together,the illustrated flexible connection be manner. Y

When the controller is moved to position 5,

ing merely a conventional showing.

In order to protect the motor 10, an electromagnetic switch 33 isprovided for controlling the actuating circuit of the line switch 15. Asshown, the actuating coils of the switch 33 are connected in series withthe primary phase windings 11 of the motor 10. Therefore, upon the flowof an excessive current in the primary windings 11 of the motor 10, theswitch 33 is actuated to interrupt the energizing circuit of theactuating coil 14 of the switch 15 to permit the latter to open.

Referring to Fig. 2, a system of acceleration for two polyphaseinduction motors is shown, embodying the principles described "for thesingle motor illustrated in Fig.1, with this difference :--The secondarywindings of the two motors are shown interconnected between tworesistors 16 and 16', each having sections 17, 18, 19 and 20 and. 17 18,19 and 20 respectively, as indicated in Fig. 2. This method ofconnecting the secondaries accomplishes even finer steps in theacceleration of the motors.

The two motors 40 and 41, having primary windings 42 and 42 andsecondary or rotor windings 43 and 43, respectively, are energized byclosing the knife-bladeswitch 44 and the subsequent closure of themain-line contactors 45 and 45'.

One winding of the rotor 43 of the motor 40 is connected to points 46and 47 of the resistor 16 that is shown at the left in Fig. 2. Theopposite phase winding ofthis rotor is connected to points 48 and 49 ofthe resistor 16 that is shown at the right in Fig. 2. It will be notedthat the connections for these windings are at the opposite points ofthe respective resistors but this arrangement is not essential to thepresent invention.

The secondary winding 43 of the motor 41 that is connected to points 51and 52 of the letthand resistor, is in o posite phase relation to thewinding 43 o the motor 40 that is connected to points 46 and 47 of saidlefthand resistor. The other secondary phase winding of motor 41 isconnectedto points 53 and 54 of the right-hand resistor. Likewise, thiswinding is in opposite phase relation to the secondary winding-of motor40 that is connected to points 48 and '49.

As described for Fig. 1, current entering at connection 52 of theleft-hand resistor of Fig. 2 will traverse one path through sections 18and 17 and a second path through sect-ions 19 and 20, emerging at point51, while that entering at tap 46 will traverse one path throughsections 17 and 20 and a second path through sections '18 and 19,emerging at tap 47; What is said for the left-hand resist-or of Fig. 2applies equally to the right-hand resistor.

A controller 55, having thirteen steps, a

to m, inclusive, is shown which, when moved to position a, is energizedin a well-known the coil of electromagnetic switch 56 is energized,thereby closing it to shunt a portion of the arms 17 and 18 of theleft-hand resistor. Accordingly, thisaction will affect the ourrent inone phase winding of motor 40 and I rent of one winding of the secondaryof motor 41, is increased, and the two motors again have the sameneutral point.

When the controller is moved to position d, the coil of electromagneticswitch 58 is energized, thereby closing this switch to shunt a portionof the arms 19 and 20 of the lefthand resistor, preferably of the sameohmic value as the previously shunted portion of this resistor. Thisaction will have the effect of again increasing the currents between thetaps 46 and 47. Likewise, the two paths between taps 51 and 52 eachhaving an equal amount shunted therefrom; these paths are balanced andthe current from the winding connected at these taps is caused tomaterially 'advance. It will be remembered that the Winding connected atthese points is located upon the motor 41, while the co-bal- ,ancedwinding is located upon the motor 40.

However, the motors are off neutral by reason of the fact that theoperating condition of the winding that is joined to taps 53 and 54 ofthe right-hand resistor is advanced with reference to the windingconnected at-points 48 and 49.

When the controller is moved to position a, the coil of electromagneticswitch 59 is energized, thereby closing this switch to shunt a portionof the arms 19 and 20 of the righthand resistor. This action will havethe same effect upon the phase winding as has been described for switch58, only upon the opposite phasewindings from those affected by thatswitch.

At this point, all arms of the resistorsare preferably balanced, therebybalancing the operating condition of all windings, and sui stantiallyexactly balancing the pulling torque of the motors; I

In each of the following positions, namely fto m, inclusive, theelectromagnetic switches 60, 61., 62, 63, 64, and 67 are closed in thesequence given, and, inasmuch as their respect' 'fects rents in thesephase windings of each motor, 1: etill maintaining the motors balanced,and

the acceleration is ad ant-ed another step. The lGlDtUHlUQ phasewindings: are illieWlS-Q Q'iFGQ 'QdlR3 911101103 and this gradualadvancewen; contiimes until full d i9: reached vih each step dightlallfeciin the motor s? e rel of this, i it in raiiway )een dwelt r 1 intee past, that Vance which tlllr: inrenrimi names in "@561 will bereadily appreciated. The important advantages derived from the hereindescribed method of acceleration n'able in raiiwayauotor operaare, in noway, ininiilites ot an conflicting, eirt in current; lJQCWQOM the twomotors.

circulating currents are posiotori-z connected in the manner describedfor the reason that, at the uni-re the aiding 5 oi the oppositeO'Ult-Clfitl to the resistor, a conpoint maintained between \ulYQl'Singpaths so that the currents will to follow their individual paths paetentra. points Without interchange llemotors.

4 inolor at) iron. the windings While the acceleration of the the majorportion or the acl unbalanced, the stepa are c, ..ated that theunbalanced feature in all ect, in an Way the operative I of the motors.I do not wish to be restricted to the specific rcuit connections orarrangements of parts rein set forth, as various modifications ercoifmay be made Without departing from J spirit and scope of my invention. Ide' therefore, that only each limitations l iinpoeed as are indicated bythe apsiren 1c UC-Hilld claims.

I c aiin as my invention: 1. In a control s stein to accelerating n10-in combination, a plurality o1? polyphase iction motors each havingprimary and secondary winding, a plurality of endless retors ach hir ng;a plurality ot the ondary windings of the motor connected thereto withbalanced or sections be tween the terminal:- of each Windin and adjacentterminals oiil'erent windings, and means for selectively shuntingportions of the resistor sections to elleet the accelerztors, incombination, a plurality of polnahase 1 i nction motors, each havingprnnar and sec-ondar; windings, tvo endless resistors aving thesecondary windings of the niiotors i crent sections of the resistor toellect the acceleration of the motors substantially without interchangeof current between the motors.

3. In a control system for polyphase motors, in combination, primary andsecondary motor windings, a resistor connected in circuit with thesecondary windings, the terminals of the windings being substantiallyevenly spaced on the resistor whereby each section of the resistor isused as a conductor for current flowing in more than one phase winding,and means for alternately and progressively short-circuiting therespective sections of the resistor connected in the circuit of thedifferent motor windings to control the current flowing in the win ings,thereby to control the speed ofthe motors.

4. In a system of control for polyphase induction motors having primaryand secondary phase windings, in combination a resistor connected to aplurality of the phase windings to provide a plurality of circuits 'witha common resistor, and means for alter- I nately and progressivelyshort-circuiting sections of the resistor located in the respectivecircuits to control the current flowing in the phase windings.

5. In a system of control for polyphase in duction motors having primaryand secondary phase windings, in combination, a loop resistor connectedto a plurality of the phase windings to provide a plurality of circuitswith a common resistor, and means for alternately and progressivelyshort-circuiting sections of the resistor located in the respectivecircuits to control the flow of current in the secondary phase windings.

6. In a system of control for polyphase induction motors having primaryand secondary phase windings, in combination, an endless resistorconnected to a plurality of the secondary phase windings, with balancedre sistor sections between the terminals of each. winding and adjacentterminals of the different windings, and means for alternately andprogressively short-circuiting portions of the respective balancedsections of the resistor connected in the circuits of the secondaryphase windings to control the flow of current in the secondary phasewindings.

In testimony whereoLI have hereunto subscribed my name this lth day ofAugust, 1925.

CHARLES LE G. FORTESCUE.

